Real-time clock and supervisor chip

STMicroelectronics, represented by Braemac , has announced a new version of its M41ST85 serial real-time clock (RTC) and Supervisor chip that includes a 32kHz crystal and comes in a low-profile, small footprint SOX28 package.

Available in 3V and 5V versions, the M41ST85MX6 integrates many common functions and draws its back-up power from an external, customer-supplied battery, commonly present in systems, thereby saving space and cost.

By integrating the crystal into the package, a better match can be achieved between the IC and the crystal, thereby improving timekeeping accuracy.

The SOX28 package offers enhanced security by isolating the crystal from tampering, plus it better shields the crystal from humidity. It also reduces assembly cost by eliminating the mounting of the crystal.

Like its SNAPHAT-packaged sibling M41ST85MH6, the M41ST85MX6 combines a serial RTC with microprocessor and NVRAM Supervisor functions. This high level of integration provides yet further cost savings.

At the heart of the M41ST85MX6 is the programmable, battery-backed RTC section, which contains counters, that track time and date with resolution ranging from hundredths of a second up to the century.

It is accessed via a 400kHz I2C interface. Built using low-power CMOS SRAM technology, the M41ST85MX6's RTC section is organised as 64 x 8 bits, of which 44 bytes are general-purpose NVRAM, while the remaining 20 bytes are the RTC registers.

The NVRAM Supervisor section can be used to "non-volatise" a low power SRAM, and its functions include an automatic battery switch-over circuit, a chip-enable gate for write protection and a battery monitor.

This enables the user to create an NVRAM by using the M41ST85MX6's back-up battery to also back-up the LPSRAM.

The M41ST85MX6's microprocessor Supervisor section includes an early power-fail warning circuit, with a 1.25V reference, and a robust reset circuit, which can be triggered by multiple sources (including two reset input pins and a power-on reset/low-voltage detect circuit).

The Watchdog can also be configured as a reset source, and is programmable for timeout periods ranging from 62.5ms to 128s.

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